This invention relates generally to a system to verify the construction of products requiring heated adhesive for assembly, and more particularly to a system for comparing the quality of adhesive-deposition operations on assembled products as well as provisions for taking corrective measures in circumstances when an adhesive deposition is such that it causes an assembled product to fall outside of an acceptable quality range.
Modern fabrication methods have increasingly taken advantage of adhesive joining to contribute to lighter-weight, more efficient assembled structures than conventional fastening approaches. Such methods have been useful in discrete manufacturing as well as continuous flow manufacturing on a conveyor line, including those used in conjunction with hot melt potting of electronic parts, product assembly with hand-guns configured to dispense hot melt adhesive, or other assembly techniques. Moreover, such approaches may be used with numerous substrates, including metals, woods, plastics, composites, paper-based materials or the like. In one example, containers for product packaging are frequently constructed from boxes that are folded from generally planar corrugated paper-based blanks or related substrates. Typical fabrication involves a series of forming operations such as those that may be performed by a packaging machine such as a case sealer or cartoner. In the present context, the terms “hot melt”, “adhesive”, hot melt adhesive” or the like are used interchangeably herein to cover various scenarios where hot melt is used; whether a more particular application (such as an adhesive) is intended will be apparent from the context.
As mentioned above, the glue application step typically involves depositing adhesive in either continuous or discrete fashion. Such adhesive deposition is subject to errors that can render the assembled product unacceptable for its intended purpose. To that end, sensors have been used to detect the presence of a deposited glue or related adhesive. While such sensors may be satisfactory for verification of the presence of glue—usually on a per-bead basis—present on a blank in a well-controlled environment, they are inadequate to check as to whether the overall pattern of glue laid down is correctly, especially in high-speed operational environments where automated assembly takes place. In addition, such sensing technology is usually not capable of accurately measuring glue quantity or placement since either many sensors must be used—one for each bead—or the sensors are subject to interference from the environment such as with thermal sensors. Thus, in situations where it is desirable to perform a more comprehensive assessment of the adhesive being deposited, single point sensors are often not adequate. Arrays of such devices arranged as imaging sensors may enhance the ability to adequately represent the deposition of adhesive onto a substrate or blank; however, such additional sensor arrays may significantly contribute to overall system cost and complexity. Moreover, to the extent that they may help assess the presence or absence of adhesive deposition in a particular location on the blank surface, they do not provide such information once direct access to the adhesive is obscured, such as by being covered by overlaid or other adjacent surfaces of the assembled item. In addition, they provide only numerical feedback regarding the glue position or length of the glue beads, for example, which can be difficult for processing equipment to filter and interpret for the user.
Furthermore, neither form of sensor is capable of providing indicia that the assembled component has been acceptably manufactured, even though adhesive is present in the desired location. For example, a hot melt adhesive applied to a box or other inner flap will clearly register on an infrared (IR) or related thermal image, even in situations where the outer flap may not have been properly adhered to the inner flap of the assembly before the adhesive cooled and set. As such, the mere detection by such a system would incorrectly give the appearance of a successfully glued component, even in situations where such is not the case. This difficulty is compounded by the fact that assembling equipment and related forming machines have tight space constraints, making it difficult to monitor actual adhesive placement immediately after it is applied.